The present invention generally relates to degrading tools, which wear during use.
Equipment for mechanical machining a workpiece often uses degrading tools to remove material from a workpiece, for example cutting tools or abrasive tools such as lapping or grinding or polishing tools. Usually the work layer of the tool is of a harder material than the workpiece, but nevertheless it degrades over its lifetime. Non-optimal work conditions result in an extended machining time, in unnecessarily fast degradation of the tool, or in damage to the workpiece, all of which are economically unfavorable. Especially workpieces of a very hard material need very expensive tools. The actual optimal work condition depends on the actual condition criteria degradation of the tool.
U.S. Pat. No. 4,786,220 discloses a cutting tool wear monitor for detecting tool wear failure of a drill by monitoring a voltage or current which is generated between drill and workpiece during drilling. It is detected when the tool is worn out.
U.S. Pat. No. 5,934,974 describes In-situ monitoring of the wear of a polishing pad for polishing semiconductor wafers by laser triangulation. The polishing tool is adjusted to compensate uneven wear of the tool.
Both U.S. patents employ effects for the measurement, which are application specific. There is a further need for more general measuring the degradation of a tool.
Now, a special field of degrading tools, which wear during use is cutting (dicing) processed semiconductor wafers for die separation with blades, which wear during use. A processed semiconductor wafer has dies comprising electronic circuits thereupon in a rectangular pattern of rows and columns. These dies are separated by a dicing blade for packaging into single housings. Typically, the blade thickness ranges from 0.015 mm to 1.3 mm. The dicing blade comprises particles of diamond as typical abrasive material within a carrier material and cut the wafer with a liquid present for cooling and removing saw dust. Three types of dicing blades are commercially available:
Sintered Diamond Blade, in which diamond particles are fused into a soft metal such as brass or copper, or incorporated by means of a metallurgical process;
Plated Diamond Blade, in which diamond particles are held in a nickel bond produced by an electroplating process; and
Resinoid Diamond Blade, in which diamond particles are held in a resin bond to create a homogeneous matrix.
Silicon wafer dicing is dominated by the plated diamond blade and the resinoid diamond blade. The resinoid diamond blade has the advantage that it is self-sharpening automatically by the cutting process.
Due to the abrasive nature of the process the dicing blade wears. A used-up or damaged dicing blade causes die damage as large particles break away from the die border. The operation parameters of the dicing blade are adjusted so that a suitable compromise of high throughput, small die damage level and reasonable blade wear is reached and usually left constant.
Usually, the dicing blade is either checked from time to time and exchanged when a certain degradation is reached, or it is exchanged after a defined number of wafers cut or a defined operation time. This conception can prevent die damage on the cost of labor for manual checking and/or too early exchange of the dicing blade, which means unnecessary blade costs and down time.
Several approaches have been undertaken to improve this compromise by detecting when the blade is considered used up. The detectable operational conditions according to the art are when the load induced on the blade by the wafer substrate reaches a predefined value or the when the blade cutting edge reaches a minimum separation distance from the work surface.
U.S. Pat. No. 6,033,288 discloses an apparatus for accumulating dicing data having a spindle motor, a spindle with a blade, a spindle driver to drive the spindle at a predetermined rotation rate, and a sensor connected to the spindle motor to determine the rotation rate of the spindle. A controller controls the spindle driver responsive to the load induced on the blade by the substrate.
According to U.S. Pat. No. 5,718,615 a semiconductor wafer dicing saw is controlled by monitoring blade exposure from a flange holding the blade during the wafer dicing process. A system measures the flange clearance using a height sensor to determine blade wear and a processor for monitors blade movement toward the wafer during the wafer dicing and stops the movement when the blade cutting edge reaches a minimum separation distance from the work surface.
Both conceptions provide unsufficient precision of the used-up condition of the blade.